The reader or audience knows something that the character ignores, and therefore the character's words and acts take on a meaning that he himself does not perceive.
In Purgatory
Of the Aeneid I speak, which was a mother to me and a nurse, as a poet: without it I would not have fixed a weight of a drachma. And for having lived there when Virgil lived, I would accept one more sun beyond what I owe to my departure from exile.
Statius praises Virgil without knowing that he has him at his side, and the reader, who knows, sees Virgil fall silent. The distance between what the character ignores and what the reader knows makes the confession a scene of tenderness and laughter.